Power Transmission Device

ABSTRACT

A power transmission device has a pressure member 5, drive-side clutch plates, driven-side clutch plates, a clutch spring 10, a separate receiving member 11, and a back-torque limiting cam. A radially-outside restricting portion restricts radially-outward movement of the receiving member 11 relative to the pressure member 5. This maintains clearance t between a side surface 11d of the receiving member 11 and an inner peripheral wall 4e of a clutch member 4.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/JP2019/000381, filed Jan. 9, 2019, which claims priority to JapaneseApplication No. 2018-002702, filed Jan. 11, 2018. The disclosures of theabove applications are incorporating herein by reference.

FIELD

The present disclosure relates to a power transmission device thatappropriately transmits or cuts off rotational power of an input memberto an output member.

BACKGROUND

In general, a motorcycle has a power transmission device forappropriately transmitting or cutting off driving power of an engine toa transmission and a driving wheel. The power transmission deviceincludes an input member coupled to the engine side. An output member iscoupled to the transmission and driving wheel side. A clutch member iscoupled to the output member. A pressure member presses clutch plates,drive-side clutch plates and driven-side clutch plates, against eachother or releases a press-contact force. The power transmission deviceis configured to transmit power by pressing the drive-side clutch platesand the driven-side clutch plates against each other. This cuts offpower by releasing the press-contact force.

For example, in a power transmission device disclosed in WO2016/024557,a receiving member is attached to the pressure member. A clutch spring,urging means, contained in the receiving member to urge the pressuremember in a direction so that the drive-side clutch plates anddriven-side clutch plates are pressed against each other. One camsurface is formed in the receiving member. The other cam surface, whichfaces the one cam surface, is formed in the clutch member. These camsurfaces constitute a back-torque limiting cam that reduces thepress-contact force between the drive-side clutch plates and thedriven-side clutch plates. The pressure member and the clutch memberrotate relative to each other when the rotation speed of the outputmember exceeds the rotation speed of the input member.

That is, if the pressure member and the clutch member rotate relative toeach other when the rotation speed of the output member exceeds therotation speed of the input member, the one cam surface and the othercam surface slide over each other. The back-torque limiting camfunctions to move the receiving member in the axial direction relativeto the pressure member. The urging force of the clutch spring applied tothe pressure member decreases. Thus, the press-contact force between thedrive-side clutch plates and the driven-side clutch plates is reduced.

SUMMARY

However, in the existing power transmission device described above, whenthe entire device, including the pressure member and the clutch member,rotates at a high speed, the receiving member is pressed against theclutch member, which is positioned radially outside, by a generatedcentrifugal force. The sliding resistance of the receiving member maybecome larger than expected. In this case, when a driver operates aclutch lever or the like to separate the pressure member from the clutchmember to disengage the clutch, release the press-contact force betweenthe clutch plates, and subsequently reengages the clutch, to press theclutch plates against each other, movement of the receiving member isslowed due to excessive sliding resistance. Thus, a problem arises inthat the response, when engaging the clutch, becomes dull and the driverexperiences an unpleasant sensation in operability due to feeling ofidle driving.

The present disclosure is designed to overcome the backgrounddeficiencies described above. It provides a power transmission devicethat can improve responsiveness when engaging a clutch. This improvesoperability by reducing the sliding resistance of a receiving member.

According to the disclosure, a power transmission device comprises aclutch housing that rotates together with rotation of an input member. Aplurality of drive-side clutch plates are attached to the clutchhousing. A clutch member has a plurality of driven-side clutch platesalternately formed with the drive-side clutch plates of the clutchhousing. They are attached with an output member. A pressure member isattached to the clutch member. The pressure member presses thedrive-side clutch plates and the driven-side clutch plates against eachother or releases a press-contact force in accordance with relativemovement to the clutch member in an axial direction. An urging membermoves the pressure member in a direction such that the drive-side clutchplates and the driven-side clutch plates are pressed against each other.A receiving member, constituted by a separate member, is attached to thepressure member. The receiving member receives an urging force of theurging member on the pressure member side. It transmits the urging forceto the pressure member. A back-torque limiting cam, constituted by apair of cam surfaces, reduces a press-contact force between thedrive-side clutch plates and the driven-side clutch plates. The pressuremember and the clutch member rotate relative to each other when arotation speed of the output member exceeds a rotation speed of theinput member. One of the cam surfaces is formed in the receiving member.The other cam surface is formed in the clutch member. The powertransmission device transmits or cuts off rotational power input to theinput member to the output member by pressing the drive-side clutchplates and the driven-side clutch plates against each other or releasingthe press-contact force. The power transmission device includes aradially-outside restricting portion that restricts radially-outwardmovement of the receiving member relative to the pressure member. Also,it maintains a clearance between a side surface of the receiving memberand the clutch member.

In the power transmission device, the radially-outside restrictingportion includes a flange portion formed on an opening side of thereceiving member. A contact portion is formed in the pressure member.The contact portion restricts the radially-outward movement of thereceiving member by making contact with the flange portion.

In the power transmission device, the contact portion is a wall surfaceextending in a rotation axis direction of the pressure member. Itconformably makes contact with a side surface of the flange portion.

In the power transmission device, the contact portion, in plan view, hasa conforming shape to an outer peripheral shape of the flange portion.

In the power transmission device, an attachment hole, for attaching thereceiving member, is formed in the pressure member. The radially-outsiderestricting portion is a radially-outside opening of the attachmenthole. It restricts the radially-outward movement by contacting thereceiving member.

In the power transmission device, the receiving member has a contactsurface with a shape conforming to the radially-outside opening of theattachment hole. The contact surface contacts with the radially-outsideopening.

The power transmission device has the radially-outside restrictingportion that restricts radially-outward movement of the receiving memberrelative to the pressure member. Thus, it maintains the clearancebetween the side surface of the receiving member and the clutch member.This makes it possible to improve responsiveness when engaging theclutch. Also, it improves operability by reducing the sliding resistanceof the receiving member.

The radially-outside restricting portion includes the flange portion.The flange portion is formed on the opening side of the receivingmember. The contact portion is formed in the pressure member. Itrestricts radially-outward movement of the receiving member by makingcontact with the flange portion. Thus, it is possible to restrict theradially-outward movement by using the flange portion of the receivingmember. It is also possible to reliably reduce the sliding resistance ofthe receiving member.

The contact portion is the wall surface extending in the rotation axisdirection of the pressure member. The contact portion contacts the sidesurface of the flange portion. Thus, it is possible to cause the flangeportion to stably contact with the contact portion. It is also possibleto more reliably reduce the sliding resistance of the receiving member.

The contact portion, in plan view, has a shape conforming to the outerperipheral shape of the flange portion. Thus, it is possible to causethe flange portion to contact the contact portion. It is also possibleto further reliably reduce the sliding resistance of the receivingmember.

The attachment hole, for attaching the receiving member, is formed inthe pressure member. The radially-outside restricting portion is theradially-outside opening of the attachment hole. It restricts theradially-outward movement by contacting the receiving member. Thus, ispossible to restrict radially-outward movement of the receiving memberby using the radially-outside opening of the attachment hole. It is alsopossible to reliably reduce the sliding resistance of the receivingmember.

The receiving member has the contact surface conforming to theradially-outside opening of the attachment hole. The contact surfacecontacts the radially-outside opening. Thus, it is possible to cause thereceiving member to stably contact the radially-outside opening, It isalso possible to more reliably reduce the sliding resistance of thereceiving member.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is longitudinal sectional view of a power transmission deviceaccording to a first embodiment.

FIG. 2 is a perspective view of the power transmission device in a statewith a clutch housing and the like removed.

FIG. 3 is a top plan view of the power transmission device of FIG. 2.

FIG. 4 is a cutaway cross-section view taken along line IV-IV in FIG. 3.

FIG. 5 is a perspective view of a clutch member of the powertransmission device.

FIG. 6 is a front plan view of the clutch member.

FIG. 7 is a rear view of the clutch member.

FIG. 8 is a perspective view of a pressure member of the powertransmission device seen from one side.

FIG. 9 is a perspective view of the pressure member seen from the otherside.

FIG. 10 is a back plan view of the pressure member.

FIG. 11 is a front plan view of the pressure member.

FIG. 12 is a perspective view of a receiving member of the powertransmission device seen from one side.

FIG. 13 is a perspective view of the receiving member seen from theother side.

FIG. 14 is a front plan view and a rear view of the receiving member.

FIG. 15 is a sectional view taken along line XV-XV in FIG. 14.

FIG. 16 is a cross-section developed view illustrating cam surfaces ofthe power transmission device.

FIG. 17 is a sectional view, taken along line XVII-XVII in FIG. 1,illustrating a radially-outside restricting portion of the powertransmission device.

FIG. 18 is a longitudinal sectional view of a power transmission deviceaccording to a second embodiment.

FIG. 19 is a perspective view of a pressure member of the powertransmission device seen from one side.

FIG. 20 is a perspective view of the pressure member seen from the otherside.

FIG. 21 is a back plan view of the pressure member.

FIG. 22 is a front plan view of the pressure member.

FIG. 23 is a front plan view and a rear plan view of a receiving memberof the power transmission device.

FIG. 24 is a sectional view taken along line XXIV-XXIV in FIG. 23.

FIG. 25 is a sectional view, taken along line XXV-XXV in FIG. 18,illustrating a radially-outside restricting portion of the powertransmission device.

FIG. 26 is a partially cutaway cross-section view of a powertransmission device according to another embodiment.

FIG. 27 is a cross-section developed view illustrating cam surfaces ofthe power transmission device.

DETAILED DESCRIPTION

Hereafter, embodiments of the present disclosure will be described indetail with reference to the drawings.

A power transmission device according to the present embodiment isdisposed in a vehicle, such as a motorcycle, and appropriately transmitsor cuts off driving power of an engine to the transmission and drivingwheel side. As illustrated in FIG. 1, the power transmission deviceincludes a clutch housing 2 with a gear 1 as an input member. A clutchmember 4 is coupled to a shaft 3 as an output member. A pressure member5 is formed on the right-end side of the clutch member 4 in the figure.Drive-side clutch plates 6 are coupled to the clutch housing 2 side.Driven-side clutch plates 7 are coupled to the clutch member 4 side. Afixing member 8, a push rod 9, clutch springs 10, as urging means, andreceiving members 11 fill out the device. In the figure, the symbol Srepresents a damper, and the symbol D represents a ball bearing.

The gear 1 can rotate around the shaft 3 when driving power (rotationalpower) transmitted from the engine is input. The gear 1 is coupled tothe clutch housing 2 by using rivets and the like. The clutch housing 2includes a cylindrical case member whose right end side in the figure isopen. A plurality of drive-side clutch plates 6 are attached to theinner peripheral wall of the clutch housing 2. Each of the drive-sideclutch plates 6 is a substantially annular plate. The plates are fitinto a spline formed in the inner peripheral surface of the clutchhousing 2. The plates 6 are rotatable together with rotation of theclutch housing 2 and slidable in the axial direction (left-rightdirections in FIG. 1).

The clutch member 4 is constituted by members disposed in the clutchhousing 2. As illustrated in FIGS. 5 to 7, the clutch member 4 includesa central hole 4 a through which the shaft 3 can be inserted. An outerperipheral wall 4 b includes splines. Bolt holes 4 c receive bolts B.Boss portions 4 d include the bolt holes 4 c. An inner peripheralsurface 4 e is formed of the outer peripheral wall 4 b. Splines areformed in each of the inner peripheral surface of the central hole 4 aand the outer peripheral surface of the shaft 3. The shaft 3 isspline-fit and coupled to the central hole 4 a. Thus, so that the shaft3 also rotates when the clutch member 4 rotates. The driven-side clutchplates 7 are fit and attached to the splines formed in the outerperipheral wall 4 b.

To be more specific, the splines, that are formed in the outerperipheral wall 4 b of the clutch member 4, include protrusions andrecesses that are integrally formed around substantially the entireperiphery of the outer peripheral wall 4 b. The driven-side clutchplates 7 engage with recessed grooves of the splines. Movement of thedriven-side clutch plates 7 in the rotational direction is restricted.Movement of the driven-side clutch plates 7 relative to the clutchmember 4 in the axial direction is allowed. The driven-side clutchplates 7 rotate together with the clutch member 4.

The driven-side clutch plates 7 are stacked alternately with thedrive-side clutch plates 6. The drive-side clutch plates 6 and thedriven-side clutch plates 7, that are adjacent to each other, can bepressed against each other or the press-contact force can be released.That is, the drive-side clutch plates 6 and the driven-side clutchplates 7 are allowed to slide in the axial direction of the clutchmember 4. When pressed by the pressure member 5 in the leftwarddirection in FIG. 1, the drive-side clutch plates 6 and the driven-sideclutch plates 7 are pressed against each other. Thus, the rotationalpower of the clutch housing 2 can be transmitted to the shaft 3 via theclutch member 4. When pressing by the pressure member 5 is relieved, thepress-contact force is released, the clutch member 4 stops following therotation of the clutch housing 2 and stops. Thus, rotational power isnot transmitted to the shaft 3.

Moreover, as illustrated in FIGS. 2 to 4, the fixing member 8 is fixedto the tip-end side of the boss portions 4 d by the bolts B, that areinserted through the bolt holes 4 c. The clutch springs 10, as an urgingmeans, are attached to the fixing member 8. To be specific, the fixingmember 8 is an annular metal member. It is fixed to the tip ends of theboss portions 4 d by using the bolts B. It is mounted in such a way thatthe receiving members 11 are positioned between the bolts B. Also, theother end portions of the clutch springs 10 are in contact with thefixing member 8.

Each of the clutch spring 10 is a coil spring. The spring 10 is mountedin such a way that, in a state of being contained in the receivingmember 11, one end is in contact with the bottom surface side of thereceiving member 11, a receiving portion 11 b. The other end is incontact with the fixing member 8. The clutch spring 10 can constantlyurge the pressure member 5 in a direction such that the drive-sideclutch plates 6 and the driven-side clutch plates 7 are pressed againsteach other in a direction such that the pressure member 5 becomes closerto the clutch member 4. Another urging means may be used as the clutchspring 10.

The pressure member 5 is attached to the clutch member 4 at a positionon the right end side in FIG. 1. Thus, the pressure member 5 is movablein the axial direction of the clutch member 4 (left-right directions inFIG. 1). The pressure member 5 can press the drive-side clutch plates 6and the driven-side clutch plates 7 against each other or release thepress-contact force in accordance with movement thereof relative to theclutch member 4 in the axial direction. To be more specific, asillustrated in FIGS. 8 to 11, the pressure member 5 includes a flangeportion 5 a that can press the drive-side clutch plates 6 and thedriven-side clutch plates 7 against each other. Attachment holes 5 b,for attaching the receiving members 11, through-holes 5 c, a centralhole 5 d, and contact portions 5 e, are included in the pressure member5.

A pressed member E is attached, via the ball bearing D as illustrated inFIG. 1, to the central hole 5 d of the pressure member 5. The pressedmember E is attached to the tip end side of the shaft 3 and is movableso as to follow the push rod 9. When a driver operates an operationmeans, such as a clutch lever or the like (not shown), this causes thepush rod 9 to protrude in the rightward direction in the figure. Thepressed member E moves in the same direction. Thus, the pressure member5 can be moved in the rightward direction in FIG. 1, direction away fromthe clutch member 4, against the urging forces of the clutch springs 10.

When the pressure member 5 moves in the rightward direction, thepress-contact force between the drive-side clutch plates 6 and thedriven-side clutch plates 7 is released. The rotational power input tothe gear 1 and the clutch housing 2 is cut off and not transmitted tothe clutch member 4 and the shaft 3. The clutch is disengaged. When thedriver stops operating the operation means, the pressure member 5 movesin the leftward direction in FIG. 1 due to the urging forces of theclutch springs 10. The drive-side clutch plates 6 and the driven-sideclutch plates 7 are pressed against each other. Thus, rotational powerinput to the gear 1 and the clutch housing 2 is transmitted to theclutch member 4 and the shaft 3. The clutch is engaged. That is, thepressure member 5 is pressing the drive-side clutch plates 6 and thedriven-side clutch plates 7 against each other or releasing thepress-contact force in accordance with movement relative to the clutchmember 4 in the axial direction.

Moreover, the attachment holes 5 b are formed in the pressure member 5at a plurality of (three) positions on the same circle at regularintervals. A receiving member 11 is attached to each of the attachmentholes 5 b. The receiving members 11, attached to the attachment holes 5b of the pressure member 5, contact with one end of the clutch spring 10and receive the urging force. It is separate from the pressure member 5.To be specific, as illustrated in FIGS. 12 to 15, the receiving member11, according to the present embodiment, has a cup-shaped member. Thecup-shaped member includes a recessed portion 11 a that contains theclutch spring 10. A receiving portion 11 b is formed in the recessedportion 11 a. The receiving portion 11 b contacts with one end portionof the clutch spring 10 and receives the urging force. A flange portion11 c contacts the pressure member 5. It transmits the urging force ofthe clutch spring 10 to the pressure member 5. A side surface 11 d is onthe cup-shaped member.

Among these, the flange portion 11 c is formed on the opening side ofthe receiving member 11. When the receiving member 11 is attached to theattachment hole 5 b, the flange portion 11 c makes contact with theopening edge of the attachment hole 5 b. After attaching the receivingmember 11 to the attachment hole 5 b, the clutch spring 10 is mountedinto the recessed portion 11 a. One end portion of the spring is incontact with the receiving portion 11 b. The urging force of the clutchspring 10 is transmitted to the pressure member 5 side via the flangeportion 11 c of the receiving members 11. The drive-side clutch plates 6and the driven-side clutch plates 7 can be pressed against each other byusing the transmitted urging force.

Moreover, the power transmission device according to the presentembodiment includes a press-contact assisting cam. The cam increases thepress-contact force between the drive-side clutch plates 6 and thedriven-side clutch plates 7. The pressure member 5 and the clutch member4 rotate relative to each other when rotational power input to the gear1, as an input member, is transmitted to the shaft 3 as an outputmember. A back-torque limiting cam reduces the press-contact forcebetween the drive-side clutch plates 6 and the driven-side clutch plates7. The pressure member 5 and the clutch member 4 rotate relative to eachother when the rotation speed of the shaft 3, as an output member,exceeds the rotation speed of the gear 1, as an input member. Camsurfaces, first to sixth cam surfaces C1 to C6, that constitute thepress-contact assisting cam and the back-torque limiting cam are shownby shading (cross-hatching) in the figures.

As illustrated in FIGS. 4 and 16, the press-contact assisting camaccording to the present embodiment is configured by the third camsurfaces C3 and the fourth cam surfaces C4. They are respectively formedin the pressure member 5 and the clutch member 4. Also, they face eachother. That is, when assembling the clutch member 4 and the pressuremember 5 together, the third cam surfaces C3, see FIG. 11, formed in thepressure member 5, and the fourth cam surfaces C4, see FIG. 7, formed inthe clutch member 4, are disposed so as to face each other. Thus, if thepressure member 5 and the clutch member 4 rotate relative to each other,when rotational power input to the gear 1 becomes capable of beingtransmitted to the shaft 3, the pressure member 5 is moved in thedirection a in FIG. 16 by the cam function of the third cam surfaces C3and the fourth cam surfaces C4. Thus, the pressure member 5 moves closerto the clutch member 4. The press-contact force between the drive-sideclutch plates 6 and the driven-side clutch plates 7 is increased.

As illustrated in FIGS. 4 and 16, the back-torque limiting cam accordingto the present embodiment is configured by the first cam surfaces C1 andthe second cam surfaces C2. They are respectively formed in thereceiving members 11 and the clutch member 4. Also, they face eachother. That is, when assembling the clutch member 4, the pressure member5, and the receiving members 11 together, the first cam surfaces C1, seeFIGS. 13 and 14, formed in the bottom side surfaces of the receivingmembers 11, and the second cam surfaces C2, see FIG. 6, formed in theclutch member 4, are disposed to face each other. Thus, if the pressuremember 5 and the clutch member 4 rotate relative to each other when therotation speed of the shaft 3 exceeds the rotation speed of the gear 1,the receiving members 11 are moved in the direction β in FIG. 16 by thecam function of the first cam surfaces C1 and the second cam surfacesC2. This reduces the urging force of the clutch springs 10 transmittedto the pressure member 5. The press-contact force between the drive-sideclutch plates 6 and the driven-side clutch plates 7 is reduced.Reduction of the press-contact force refers to a state whererotational-power transmitting capacity is reduced due to sliding of thedrive-side clutch plates 6 and the driven-side clutch plates 7 over eachother.

Moreover, as illustrated in FIG. 14, in each of the receiving members 11according to the present embodiment, the fifth cam surface C5 is formedon a side opposite from the first cam surface C1. The sixth cam surfacesC6, see FIG. 11, each facing the fifth cam surface C5, are formed in thepressure member 5. That is, in both side surfaces of the bottom portionof each of the receiving members 11, the first cam surface C1 and thefifth cam surface C5 are respectively formed. The back-torque limitingcam includes the first cam surfaces C1, the second cam surfaces C2, thefifth cam surfaces C5, and the sixth cam surfaces C6.

When assembling the clutch member 4, the pressure member 5, and thereceiving members 11 together, the first cam surfaces C1, formed in thereceiving members 11, and the second cam surfaces C2, formed in theclutch member 4, are disposed to face each other. The fifth cam surfacesC5, formed in the receiving members 11, and the sixth cam surfaces C6,formed in the pressure member 5, are disposed to face each other. Thus,if the pressure member 5 and the clutch member 4 rotate relative to eachother when the rotation speed of the shaft 3 exceeds the rotation speedof the gear 1, the receiving members 11 are moved in the direction 13 inFIG. 16 by the cam function of the first cam surfaces C1 and the secondcam surfaces C2 and the cam function of the fifth cam surfaces C5 andthe sixth cam surfaces C6. Thus, the press-contact force between thedrive-side clutch plates 6 and the driven-side clutch plates 7 isreduced.

Thus, when the back-torque limiting cam functions, the receiving members11 receive both of the cam function of the first cam surfaces C1 and thesecond cam surfaces C2 and the cam function of the fifth cam surfaces C5and the sixth cam surfaces C6. Although the back-torque limiting camaccording to the present embodiment includes the fifth cam surfaces C5and the sixth cam surfaces C6, in addition to the first cam surfaces C1and the second cam surfaces C2, the back-torque limiting cam may haveonly the first cam surfaces C1 and the second cam surfaces C2.

Here, the power transmission device, according to the presentembodiment, includes a radially-outside restricting portion. Itrestricts radially-outward movement of the receiving member 11 relativeto the pressure member 5, in a direction outward from the rotationalcenter of the pressure member 5. Also, it maintains the clearance t (seeFIG. 1) between the side surface 11 d of the receiving members 11 andthe inner peripheral surface 4 e of the clutch member 4. To be specific,as illustrated in FIGS. 1 and 17, the radially-outside restrictingportion according to the present embodiment includes the flange portion11 c, formed on the opening side of each of the receiving members 11,and the contact portion 5 e, formed in the pressure member 5. Thecontact portion 5 e restricts radially-outward movement of the receivingmember 11 by making contact with the flange portion 11 c.

That is, in a state where the receiving member 11 is attached to theattachment hole 5 b, the contact portion 5 e is formed at a positionradially outside of the flange portion 11 c of the receiving member 11.When the pressure member 5 and the like rotate at a high speed and thereceiving member 11 receives a radially-outward centrifugal force, theflange portion 11 c contacts the contact portion 5 e and resists thecentrifugal force. Therefore, it is possible to avoid radially-outwardmovement of the receiving member 11. This maintains the clearance t(gap) between the side surface 11 d of the receiving member 11 and theinner peripheral surface 4 e of the clutch member 4.

The contact portion 5 e according to the present embodiment isintegrally formed on the radially outer side of the attachment hole 5 bof the pressure member 5. It includes a wall surface extending in therotation axis direction of the pressure member 5, left-right directionsin FIG. 1. The wall contacts a radially-outer side surface 11 ca, outerperipheral end surface, of the flange portion 11 c of the receivingmember 11. Moreover, as illustrated in FIG. 17, the contact portion 5 e,according to the present embodiment, has a shape conforming to the outershape of the flange portion 11 c in plan view. The radially-outer sidesurface 11 ca of the flange portion 11 c contacts substantially theentire area of the contact portion 5 e.

The present embodiment includes the radially-outside restricting portionthat can restrict radially-outward movement of the receiving member 11relative to the pressure member 5. It maintains the clearance t betweenthe side surface 11 d of the receiving member 11 and the clutch member4. Therefore, with the present embodiment, it is possible to prevent thereceiving member 11 from sliding over the inner peripheral surface 4 eof the clutch member 4. Also, it is possible to improve responsivenesswhen engaging the clutch. Further, it improves operability by reducingthe sliding resistance of the receiving member 11.

Moreover, the radially-outside restricting portion according to thepresent embodiment includes the flange portion 11 c formed on theopening side of the receiving member 11. The contact portion 5 e, formedin the pressure member 5, restricts radially-outward movement of thereceiving member 11 by contacting the flange portion 11 c. Thus, it ispossible to restrict the radially-outward movement by using the flangeportion 11 c of the receiving member 11. Thus, it is possible toreliably reduce the sliding resistance of the receiving member 11.

Moreover, the contact portion 5 e, according to the present embodiment,includes the wall surface extending in the rotation axis direction ofthe pressure member 5. The wall contacts the side surface 11 ca of theflange portion 11 c. Thus, it is possible to cause the flange portion 11c to stably contact the contact portion 5 e. Thus, and it is possible tomore reliably reduce the sliding resistance of the receiving member 11.Furthermore, the contact portion 5 e, according to the presentembodiment, has a shape conforming to the outer shape of the flangeportion 11 c, in plan view. Thus, it is possible to cause the flangeportion 11 c to stably contact with the contact portion 5 e.Accordingly, it is possible to further reliably reduce the slidingresistance of the receiving member 11.

Next, a power transmission device according to a second embodiment willbe described.

As with the first embodiment, a power transmission device according tothe present embodiment is disposed in a vehicle, such as a motorcycle.It appropriately transmits or cuts off driving power of an engine to thetransmission and driving wheel side. As illustrated in FIG. 18, thepower transmission device includes a clutch housing 2 with a gear 1 asan input member. A clutch member 4 coupled to a shaft 3 is an outputmember. A pressure member 5 is formed on the right-end side of theclutch member 4 in the figure. Drive-side clutch plates 6 are coupled tothe clutch housing 2. Driven-side clutch plates 7 are coupled to theclutch member 4 side. A fixing member 8, a push rod 9, clutch springs10, as an urging means, and receiving members 11 are illustrated.Elements that are the same as those of the first embodiment will bedenoted by the same numerals, and detailed descriptions of such elementswill be omitted.

The pressure member 5 is attached to the clutch member 4 at a positionon the right end side in FIG. 18. The pressure member 5 is movable inthe axial direction of the clutch member 4, left-right directions inFIG. 18. The pressure member 5 can press the drive-side clutch plates 6and the driven-side clutch plates 7 against each other or release thepress-contact force in accordance with movement relative to the clutchmember 4 in the axial direction. To be more specific, as illustrated inFIGS. 19 to 22, the pressure member 5, according to the presentembodiment, includes a flange portion 5 a that can press the drive-sideclutch plates 6 and the driven-side clutch plates 7 against each other.Attachment holes 5 b attach the receiving members 11. Through-holes 5 c,and a central hole 5 d are present.

The receiving member 11 is attached to the attachment hole 5 b of thepressure member 5. It contacts with one end of the clutch spring 10 andreceive the urging force. It is separate from the pressure member 5. Tobe specific, as illustrated in FIGS. 23 and 24, the receiving member 11,according to the present embodiment, is a cup-shaped member. It includesa recessed portion 11 a that contains the clutch spring 10. Thereceiving portion 11 b is formed in the recessed portion 11 a. Thereceiving portion 11 b contacts one end portion of the clutch spring 10and receives an urging force. A flange portion 11 c contacts thepressure member 5. The flange portion 11 c transmits the urging force ofthe clutch spring 10 to the pressure member 5. A contact surface 11 eand a radially-outer side surface 11 f constitute the outer peripheralsurface of the receiving member 11.

Here, the power transmission device, according to the presentembodiment, includes a radially-outside restricting portion thatrestrict radially-outward movement of the receiving member 11 relativeto the pressure member 5, in a direction outward from the rotationalcenter of the pressure member 5, It maintains the clearance t (see FIG.18) between the side surface 11 d of the receiving members 11 and theinner peripheral surface 4 e of the clutch member 4. To be specific, asillustrated in FIGS. 22 and 25, the radially-outside restricting portionaccording to the present embodiment is a radially-outside opening 5 f ofthe attachment hole 5 b of the pressure member 5. It is configured torestrict radially-outward movement by contact with the receiving member11.

The radially-outside opening 5 f is a part whose opening dimension issmaller than the width of the receiving member 11. It conforms to thecontact surface 11 e of the receiving member 11. That is, in a statewhere the receiving member 11 is attached to the attachment hole 5 b,the contact surface 11 e of the receiving member 11 contacts theradially-outside opening 5 f of the attachment hole 5 b. When thepressure member 5 and the like rotate at a high speed and the receivingmember 11 receives a radially-outward centrifugal force, the contactsurface 11 e contacts the radially-outside opening 5 f and resists thecentrifugal force. Therefore, it is possible to avoid radially-outwardmovement of the receiving member 11. This maintains the clearance t(gap) between the radially-outer side surface 11 f of the receivingmember 11 and the inner peripheral surface 4 e of the clutch member 4.

The contact surface 11 e of the receiving member 11, according to thepresent embodiment, has a shape conforming to the radially-outsideopening 5 f of the attachment hole 5 b. The contact surface 11 e isconfigured to contact the radially-outside opening 5 f. To be specific,the contact surface 11 e includes two surfaces in two directions,between which the radially-outer side surface 11 f is interposed. Thecontact surface 11 e is configured to contact the opening 5 f. Thus, itis possible to maintain the clearance t between the radially-outer sidesurface 11 f of the receiving member 11 and the inner peripheral surface4 e of the clutch member 4 in a state where the contact surface lie andthe opening 5 f are in contact with each other.

The present embodiment includes the radially-outside restricting portionthat restricts radially-outward movement of the receiving member 11relative to the pressure member 5. This maintains the clearance tbetween the radially-outer side surface 11 f of the receiving member 11and the clutch member 4. Therefore, with the present embodiment, it ispossible to prevent the receiving member 11 from sliding over the innerperipheral surface 4 e of the clutch member 4. This improvesresponsiveness when engaging the clutch and improves operability byreducing the sliding resistance of the receiving member 11.

Moreover, the radially-outside restricting portion, according to thepresent embodiment, includes radially-outside opening 5 f of theattachment hole 5 b. It restricts radially-outward movement by contactwith the receiving member 11. Thus, it is possible to restrict theradially-outward movement of the receiving member 11 by using theradially-outside opening 5 f of the attachment hole 5 b. This reliablyreduces the sliding resistance of the receiving member 11. Furthermore,the receiving member 11, according to the present embodiment, has thecontact surface lie conforming to the radially-outside opening 5 f ofthe attachment holes 5 b. The contact surface lie contacts theradially-outside opening 5 f. Thus, it is possible to cause thereceiving member 11 to stably make contact with the radially-outsideopening 5 f. This reliably reduces the sliding resistance of thereceiving member 11.

The present disclosure is not limited to the embodiments describedabove. For example, as illustrated in FIGS. 26 and 27, the presentdisclosure may be applied to a power transmission device that does nothave the press-contact assisting cam (the third cam surfaces C3 and thefourth cam surfaces C4 in the first and second embodiments). Even inthis case, the power transmission device includes the radially-outsiderestricting portion that can restrict radially-outward movement of thereceiving member 11 relative to the pressure member 5. This maintainsthe clearance t between the side surface (11 d, 11 f) of the receivingmember 11 and the inner peripheral surface 4 e of the clutch member 4.Thus, it is possible to prevent the receiving member 11 from slidingover the inner peripheral surface 4 e of the clutch member 4. It is alsopossible to improve responsiveness when engaging the clutch and improveoperability by reducing the sliding resistance of the receiving member11.

Moreover, in the present embodiment, a plurality of (three) receivingmembers 11 are attached to the pressure member 5. The radially-outsiderestricting portion restricts radially-outward movement of each of thereceiving members 11. However, only one or some selected receivingmembers 11 may be configured to be restricted by the radially-outsiderestricting portion. The number of receiving members 11 attached and theshape of each of the receiving members 11 are not limited. The powertransmission device according to the present disclosure can be used as amultiple disc clutch for a motorcycle, an automobile, a three-wheeled orfour-wheeled ATV, a general-purpose machine, or the like.

The present disclosure is applicable to any power transmission devicethat has a different outer shape or that has additional functions, aslong as the power transmission device has a radially-outside restrictingportion that can restrict radially-outward movement of a receivingmember relative to a pressure member and can maintain a clearancebetween a side surface of the receiving member and a clutch member.

The present disclosure has been described with reference to thepreferred embodiment. Obviously, modifications and alternations willoccur to those of ordinary skill in the art upon reading andunderstanding the preceding detailed description. It is intended thatthe present disclosure be construed to include all such alternations andmodifications insofar as they come within the scope of the appendedclaims or their equivalents.

What is claimed is:
 1. A power transmission device comprising: a clutchhousing that rotates together with rotation of an input member andincludes a plurality of drive-side clutch plates; a clutch member with aplurality of driven-side clutch plates that are alternately formed withthe drive-side clutch plates of the clutch housing and the clutch membercoupled with an output member; a pressure member attached to the clutchmember, the pressure member pressing the drive-side clutch plates andthe driven-side clutch plates against each other or releasing apress-contact force in accordance with movement relative to the clutchmember in an axial direction; urging member urges the pressure member ina direction so that the drive-side clutch plates and the driven-sideclutch plates are pressed against each other; a separate receivingmember is attached to the pressure member, the receiving member receivesan urging force of the urging member on the pressure member side, andthe receiving member transmits the urging force to the pressure member;and a back-torque limiting cam including a pair of cam surfaces thatreduce a press-contact force between the drive-side clutch plates andthe driven-side clutch plates if the pressure member and the clutchmember rotate relative to each other when a rotation speed of the outputmember exceeds a rotation speed of the input member, one of the camsurfaces formed in the receiving member, the other cam surface formed inthe clutch member; the power transmission device transmits or cuts offrotational power input to the input member to the output member bypressing the drive-side clutch plates and the driven-side clutch platesagainst each other or releasing the press-contact force; and the powertransmission device includes a radially-outside restricting portionrestricting radially-outward movement of the receiving member relativeto the pressure member, the radially-outside restricting portionmaintaining a clearance between a side surface of the receiving memberand the clutch member.
 2. The power transmission device according toclaim 1, wherein the radially-outside restricting portion includes aflange portion formed on an opening side of the receiving member, and acontact portion formed in the pressure member, the contact portionrestricting the radially-outward movement of the receiving member bycontact with the flange portion.
 3. The power transmission deviceaccording to claim 2, wherein the contact portion is a wall surfaceextending in a rotation axis direction of the pressure member, the wallcontacts a side surface of the flange portion.
 4. The power transmissiondevice according to claim 3, wherein the contact portion, in plan view,has a shape conforming to an outer peripheral shape of the flangeportion.
 5. The power transmission device according to claim 1, furthercomprising an attachment hole for attaching the receiving member isformed in the pressure member, and the radially-outside restrictingportion includes a radially-outside opening of the attachment hole, theradially-outward restriction portion restricts the radially-outwardmovement by contact with the receiving member.
 6. The power transmissiondevice according to claim 5, wherein the receiving member has a contactsurface with a shape conforming to the radially-outside opening of theattachment hole, and the contact surface contacts the radially-outsideopening.